8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes four planetary gear sets having five torque-transmitting mechanisms, two fixed interconnections and two grounded members. The powertrain includes an engine and torque converter that is continuously connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The five torque-transmitting mechanisms provide interconnections between various gear members, and are operated in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/909,121, filed Mar. 30, 2007, and which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a power transmission having fourplanetary gear sets that are controlled by five torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

The present invention provides an improved transmission having fourplanetary gear sets controlled to provide at least eight forward speedratios and at least one reverse speed ratio.

The transmission family of the present invention has four planetary gearsets, each of which includes a first, second and third member, whichmembers may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second, third and fourth gear sets in thisdescription and in the claims, these sets may be counted “first” to“fourth” in any order in the drawing (i.e., left to right, right toleft, etc.). Additionally, the first, second or third members of eachgear set may be counted “first” to “third” in any order in the drawing(i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the ring gearmember of the second planetary gear set with the sun gear member of thethird planetary gear set.

A second interconnecting member continuously connects the sun gearmember of the first planetary gear set with the sun gear member of thefourth planetary gear set.

The ring gear member of the first planetary gear set and the sun gearmember of the second planetary gear set are continuously connected witha stationary member (transmission housing/casing).

The input member is continuously connected with the planet carrierassembly member of the second planetary gear set.

The output member is continuously connected with the planet carrierassembly member of the first planetary gear set.

A first torque transmitting device, such as a clutch, selectivelyconnects the planet carrier assembly member of the first planetary gearset with the planet carrier assembly member of the third planetary gearset.

A second torque transmitting device, such as a clutch, selectivelyconnects the planet carrier assembly member of the second planetary gearset with the planet carrier assembly member of the fourth planetary gearset.

A third torque transmitting device, such as a clutch, selectivelyconnects the ring gear member of the third planetary gear set with thering gear member of the fourth planetary gear set.

A fourth torque transmitting device, such as a clutch, selectivelyconnects the ring gear member of the third planetary gear set with theplanet carrier assembly member of the fourth planetary gear set.

A fifth torque transmitting device, such as a clutch, selectivelyconnects the planet carrier assembly member of the third planetary gearset with the planet carrier assembly member of the fourth planetary gearset.

The five torque-transmitting mechanisms are selectively engageable incombinations of three to yield at least eight forward speed ratios andat least one reverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a schematic representation an alternative arrangement of thepowertrain of FIG. 1 a;

FIG. 1 c is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIGS. 1 a and 1 b; and

FIG. 1 d is a schematic representation of the powertrains of FIGS. 1 aand 1 b depicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes four planetary gear sets20, 30, 40 and 50.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the ring gear member 34 and the sun gear member 32.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear set 50 includes a sun gear member 52, a ring gearmember 54, and a planet carrier assembly member 56. The planet carrierassembly member 56 includes a plurality of pinion gears 57 mounted on acarrier member 59 and disposed in meshing relationship with both thering gear member 54 and the sun gear member 52.

The planetary gear arrangement also includes five torque-transmittingmechanisms 80, 82, 84, 85 and 86. The torque transmitting devices 80,82, 84, 85 and 86 are rotating-type torque-transmitting mechanisms,commonly termed clutches.

The input member 17 is continuously connected with the planet carrierassembly member 36 of the planetary gear set 30. The output member 19 iscontinuously connected with the planet carrier assembly member 26 of theplanetary gear set 20.

The ring gear member 24 of the planetary gear set 20 and the sun gearmember 32 of the planetary gear set 30 are continuously connected withthe transmission housing 60.

A first interconnecting member 70 continuously connects the ring gearmember 34 of the planetary gear set 30 with the sun gear member 42 ofthe planetary gear set 40. A second interconnecting member 72continuously connects the sun gear member 22 of the planetary gear set20 with the sun gear member 52 of the planetary gear set 50.

A first torque transmitting device, such as clutch 80, selectivelyconnects the planet carrier assembly member 26 of the planetary gear set20 with the planet carrier assembly member 46 of the planetary gear set40. A second torque transmitting device, such as clutch 82, selectivelyconnects the planet carrier assembly member 36 of the planetary gear set30 with the planet carrier assembly member 56 of the planetary gear set50. A third torque transmitting device, such as clutch 84, selectivelyconnects the ring gear member 44 of the planetary gear set 40 with thering gear member 54 of the planetary gear set 50. A fourth torquetransmitting device, such as clutch 85, selectively connects the ringgear member 44 of the planetary gear set 40 with the planet carrierassembly member 56 of the planetary gear set 50. A fifth torquetransmitting device, such as clutch 86, selectively connects the planetcarrier assembly member 46 of the planetary gear set 40 with the planetcarrier assembly member 56 of the planetary gear set 50.

As shown in FIG. 1 c, and in particular the truth table disclosedtherein, the torque-transmitting mechanisms are selectively engaged incombinations of three to provide at least eight forward speed ratios andat least one reverse speed ratio, all with single transition sequentialshifts, and including two overdrive ratios.

As set forth above, the engagement schedule for the torque-transmittingmechanisms is shown in the truth table of FIG. 1 c. The chart of FIG. 1c describes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.59, while the step ratio between the reversespeed ratio and first forward ratio is −0.68.

Referring to FIG. 1 b, an alternative arrangement of the powertrain ofFIG. 1 a is show, wherein like reference numerals are used to refer tolike components from FIG. 1 a, with a suffix “A” added to the referencenumerals in the transmission of FIG. 1 b. All elements function asdescribed above with reference to FIG. 1 a, but are repositioned.

Referring to FIG. 1 d, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive 16, a first planetary gear set 20B having three nodes: afirst node 22B, a second node 26B and a third node 24B; a secondplanetary gear set 30B having three nodes: a first node 32B, a secondnode 36B and a third node 34B; a third planetary gear set 40B havingthree nodes: a first node 42B, a second node 46B and a third node 44B;and a fourth planetary gear set 50B having three nodes; a first node52B, a second node 56B and a third node 54B.

The input member 17 is continuously connected with node 36B. The outputmember 19 is continuously connected with node 26B. The node 24B iscontinuously connected with the transmission housing 60. The node 32B iscontinuously connected with the transmission housing 60.

The node 34B is continuously connected with node 42B. The node 22B iscontinuously connected with node 52B.

A first torque-transmitting device, such as clutch 80, selectivelyconnects the node 26B with the node 46B. A second torque-transmittingdevice, such as clutch 82, selectively connects the node 36B with node56B. A third torque-transmitting device, such as clutch 84, selectivelyconnects the node 44B with node 54B. A fourth torque-transmittingdevice, such as clutch 85, selectively connects node 44B with node 56B.A fifth torque-transmitting device, such as clutch 86, selectivelyconnects node 46B to node 56B.

To establish ratios, three torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row. For example, to establish reversegear, the clutches 80, 84 and 85 are engaged. The clutch 80 engages thenode 26B with the node 46B. The clutch 84 engages the node 44B with thenode 54B. The clutch 85 engages the node 44B with the node 56B.Likewise, the eight forward speed ratios are achieved through differentcombinations of clutch engagement as per FIG. 1 c.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havingfirst, second and third members; a first interconnecting membercontinuously connecting said third member of said second planetary gearset with said first member of said third planetary gear set; a secondinterconnecting member continuously connecting said first member of saidfirst planetary gear set with said first member of said fourth planetarygear set; said third member of said first planetary gear set and saidfirst member of said second planetary gear set being continuouslyconnected with a stationary member; and five torque-transmittingdevices, wherein each of said five torque-transmitting devicesselectively interconnects a respective one of said members of saidplanetary gear sets with another respective one of said members of saidplanetary gear sets with other members of said planetary gear sets, saidfive torque-transmitting devices being engaged in combinations of threeto establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member. 2.The transmission of claim 1, wherein a first of said five torquetransmitting devices is operable for selectively connecting said secondmember of said first planetary gear set with said second member of saidthird planetary gear set.
 3. The transmission of claim 2, wherein asecond of said five torque transmitting devices is operable forselectively connecting said second member of said second planetary gearset with said second member of said fourth planetary gear set.
 4. Thetransmission of claim 3, wherein a third of said five torquetransmitting devices is operable for selectively connecting said thirdmember of said third planetary gear set with said third member of saidfourth planetary gear set.
 5. The transmission of claim 4, wherein afourth of said five torque transmitting devices is operable forselectively connecting said third member of said third planetary gearset with said second member of said fourth planetary gear set.
 6. Thetransmission of claim 5, wherein a fifth of said five torquetransmitting device is operable for selectively connecting said secondmember of said third planetary gear set with said second member of saidfourth planetary gear set.
 7. The transmission defined in claim 1,wherein said first, second, third, fourth and fifth torque-transmittingmechanisms comprise clutches.
 8. The transmission of claim 6, whereinsaid first, second and third members of said first, second, third andfourth planetary gear sets comprise a sun gear member, a planet carrierassembly member and a ring gear member, respectively.
 9. Thetransmission defined in claim 1, wherein said input member iscontinuously interconnected with said second member of said secondplanetary gear set, and said output member is continuouslyinterconnected with said second member of said first planetary gear set.10. A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havinga first, second and third member; said input member being continuouslyinterconnected with said second member of said second planetary gearset; said output member being continuously interconnected with saidsecond member of said first planetary gear set; said third member ofsaid first planetary gear set and said first member of said secondplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidthird member of said second planetary gear set with said first member ofsaid third planetary gear set; a second interconnecting membercontinuously connecting said first member of said first planetary gearset with said first member of said fourth planetary gear set; a firsttorque transmitting device selectively connecting said second member ofsaid first planetary gear set with said second member of said thirdplanetary gear set; a second torque transmitting device selectivelyconnecting said second member of said second planetary gear set withsaid second member of said fourth planetary gear set; a third torquetransmitting device selectively connecting said third member of saidthird planetary gear set with said third member of said fourth planetarygear set; a fourth torque transmitting device selectively connectingsaid third member of said third planetary gear set with said secondmember of said fourth planetary gear set; a fifth torque transmittingdevice selectively connecting said second member of said third planetarygear set with said second member of said fourth planetary gear set; saidtorque-transmitting mechanisms being engaged in combinations of three toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.
 11. Amulti-speed transmission comprising: an input member; an output member;first, second, third and fourth planetary gear sets each having a sungear member, planet carrier assembly member and ring gear member; saidinput member being continuously interconnected with said planet carrierassembly member of said second planetary gear set; said output memberbeing continuously interconnected with said planet carrier assemblymember of said first planetary gear set; said ring gear member of saidfirst planetary gear set and said sun gear member of said secondplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting said ringgear member of said second planetary gear set with said sun gear memberof said third planetary gear set; a second interconnecting membercontinuously connecting said sun gear member of said first planetarygear set with said sun gear member of said fourth planetary gear set; afirst torque transmitting device selectively connecting said planetcarrier assembly member of said first planetary gear set with saidplanet carrier assembly member of said third planetary gear set; asecond torque transmitting device selectively connecting said planetcarrier assembly member of said second planetary gear set with saidplanet carrier assembly member of said fourth planetary gear set; athird torque transmitting device selectively connecting said ring gearmember of said third planetary gear set with said ring gear member ofsaid fourth planetary gear set; a fourth torque transmitting deviceselectively connecting said ring gear member of said third planetarygear set with said planet carrier assembly member of said fourthplanetary gear set; a fifth torque transmitting device selectivelyconnecting said planet carrier assembly member of said third planetarygear set with said planet carrier assembly member of said fourthplanetary gear set; said torque-transmitting mechanisms being engaged incombinations of three to establish at least eight forward speed ratiosand at least one reverse speed ratio between said input member and saidoutput member.